Diffraction · 衍射 (Diffraction)
| English | 中文 | Pinyin · 拼音 |
|---|---|---|
| diffraction/dɪˈfrækʃn/ | 衍射 | yǎn shè |
You hear around corners, but you can't see around them
- Someone talks in the next room and you hear them, even without a straight line to your ear.
- Yet you can't see around the same corner. Why the difference?
- Waves bend and spread as they pass through gaps and around edges — diffraction 衍射.
- How much they spread depends on the gap size compared with the wavelength.
你能听到拐角后的声音,却看不到拐角后的东西
- 隔壁房间有人说话,你能听到,即使没有一条直线通到你耳朵。
- 可你却看不到同一个拐角后的东西。为什么有差别?
- 波在穿过缝隙和绕过边缘时会弯曲、扩散——衍射。
- 它们扩散多少,取决于缝隙大小与波长的比较。
Waves spread through gaps
- When a wave passes through a gap or past an edge, it fans out into the space beyond.
- This spreading is diffraction, and it happens for all waves.
- Straight (plane) waves become curved as they emerge from a narrow gap.
- It is why sound reaches you around a doorway or a wall.
波穿过缝隙扩散
- 当波穿过一个缝隙或经过一个边缘时,它向缝隙之外的空间散开。
- 这种散开就是衍射,它对所有波都发生。
- 直(平面)波从窄缝隙出来时变成弯曲的波。
- 这就是声音能绕过门口或墙到达你的原因。
Diffraction is the: · 衍射是指：
Diffraction is the spreading of waves as they pass gaps or edges. · 衍射是波通过缝隙或边缘时的扩散现象。
Diffraction happens as waves pass through gaps or around ____. · 衍射发生在波通过缝隙或绕过____时。
Waves spread out at gaps and around edges. · 波在缝隙处扩散并绕过边缘。
Gap size matters most
- Diffraction is greatest when the gap is about the same size as the wavelength.
- A gap much wider than the wavelength barely spreads the wave.
- A gap around the wavelength's size spreads it almost in a semicircle.
- So a narrow gap (relative to $\lambda$) causes the most bending.
缝隙大小最重要
- 当缝隙约与波长相同大小时,衍射最强。
- 比波长宽得多的缝隙几乎不使波散开。
- 约波长大小的缝隙几乎把波散成半圆。
- 所以(相对 $\lambda$ 而言)窄的缝隙造成最多弯曲。
Diffraction is greatest when the gap width is: · 当缝隙宽度为以下哪种情况时，衍射最显著：
Spreading is greatest when the gap is about the size of the wavelength. · 当缝隙大小约等于波长时，扩散最明显。
Select all · 所有 true statements about diffraction. · 选择关于衍射的所有正确陈述。
Diffraction spreads waves, is greatest at gap ≈ wavelength, and is why sound bends around corners. A huge gap diffracts least. · 衍射使波扩散，在缝隙≈波长时最显著，这也是声音能绕弯的原因。巨大的缝隙衍射最少。
Why sound bends but light doesn't (usually)
- Sound has a wavelength of about a metre, similar to doorways — so it diffracts strongly.
- Light's wavelength is tiny (under a micrometre), so everyday gaps barely diffract it.
- That's why you hear around corners but light casts sharp shadows.
- Shrink a slit to light's wavelength, though, and light diffracts too (next lesson).
为什么声音弯曲而光(通常)不弯
- 声的波长约一米,与门口相近——所以它强烈衍射。
- 光的波长极小(不到一微米),所以日常缝隙几乎不使它衍射。
- 这就是为什么你能听到拐角后的声音,而光投下清晰的影子。
- 不过,把缝隙缩到光的波长,光也会衍射(下一节)。
More or less diffraction? · 更多或更少的衍射？
Waves spread most when the gap is comparable to their wavelength. Sort each case. · 当缝隙大小与波长相当时，波扩散最明显。对每种情况进行排序。
Sound diffracts strongly around doorways because its wavelength is similar to a doorway's size. · 声波能强烈地绕过门口，因为其波长与门口尺寸相似。
Sound's metre-scale wavelength matches everyday gaps, so it diffracts strongly. · 声波的米级波长与日常缝隙匹配，因此衍射强烈。
Why does light usually cast sharp shadows through everyday gaps? · 为什么光通常通过日常缝隙投射出清晰的阴影？
Light's tiny wavelength means everyday gaps are far too big to diffract it much. · 光的波长极小，意味着日常缝隙太大，无法使其产生明显衍射。
Diffraction is strongest when the gap width is comparable to the wavelength, not when the gap is huge. This is exactly why sound (long wavelength) diffracts around everyday obstacles but light (tiny wavelength) usually doesn't — the gap is far larger than light's wavelength.
当缝隙宽度与波长相近时衍射最强,而非缝隙巨大时。这正是为什么声(长波长)绕日常障碍衍射,而光(极小波长)通常不衍射——缝隙远大于光的波长。
Sound (wavelength ~$1\ \text{m}$) and light (wavelength ~$5\times10^{-7}\ \text{m}$) both pass through a $1\ \text{m}$ doorway.
- The doorway ≈ the sound wavelength, so sound diffracts strongly — you hear around it.
- The doorway is millions of times the light wavelength, so light barely diffracts.
声(波长 ~$1\ \text{m}$)和光(波长 ~$5\times10^{-7}\ \text{m}$)都穿过一个 $1\ \text{m}$ 的门口。
- 门口 ≈ 声的波长,所以声强烈衍射——你能听到它绕过来。
- 门口是光波长的几百万倍,所以光几乎不衍射。
Diffraction is the spreading of waves through gaps and around edges. It is greatest when the gap ≈ the wavelength. Because sound has a metre-scale wavelength it diffracts around everyday obstacles, while light's tiny wavelength means it usually casts sharp shadows.
衍射是波穿过缝隙和绕过边缘的散开。当缝隙 ≈ 波长时最强。因为声有米级波长,它绕日常障碍衍射,而光极小的波长意味着它通常投下清晰的影子。